1. Field of the Invention
The present invention relates to a digital electronic device, and more particularly, to a digital electronic device capable of suppressing common-mode noise.
2. Description of the Prior Art
With the increasing operation speed and clock frequency of high-speed digital circuits, differential microstrip lines and strip lines have been widely used for transmitting differential signals. Ideally, a differential transmission line is characterized by low crosstalk effect and lower electromagnetic radiation. However, discontinuous structures, such as bends, through holes, etc. of an electronic circuit configured to reduce the required area or asymmetric magnitude and phase of an outputted differential signal, may result in the common-mode noise. The common-mode noise will be transmitted via the ground plane to the edge of the plate, the connected leads and the shielding metal, causing serious problems concerning electromagnetic compatibility and electromagnetic interference. Moreover, the differential transmission line is not a perfect metal and thus has a limited conductivity, and there is a dissipative medium existing in the differential transmission line. Accordingly, frequency dependent transmission line loss occurs during the time when signals are transmitted, causing interbit interference. The interbit interference does great damage to the eye diagram (which represents signal quality), leading the logic circuit to make erroneous decisions.
Therefore, a digital electronic device capable of effectively suppressing common-mode noise and meanwhile improving the eye diagram needs to appear in the high-speed digital circuits.